Method and system for handling a network-identified emergency session

ABSTRACT

The invention relates to a method and system for establishing an emergency session in a communication system which includes at least one user equipment and one or more network entities involved in establishing an emergency session. When the user equipment initiates a session by sending a message to a network entity indicating an identifier, e.g. the call number or logical name of a called entity, one of said network entities analyses the received identifier. When detecting that the session to be initiated is an emergency session, an information is returned to the user equipment for informing the latter that the initiated session is an emergency session. The user equipment thereupon initiates the execution of an emergency session. Thus, even when the user equipment is unable to detect, by itself, that the intended session is an emergency session, the network will inform the user equipment on the emergency session for ensuring appropriate handling thereof.

FIELD AND BACKGROUND OF THE INVENTION

The invention generally relates to the connection of emergency sessionssuch as emergency calls.

Emergency calls shall be supported in IP Multimedia networks (IMS). TheUE (User Equipment) may usually be able to indicate in the initialsession setup (e.g. in the INVITE message of SIP) that the session is anemergency session.

However, there may be situations where the initial session setup messageis just sent with an ordinary number and there is no indication aboutthe emergency. These situations may e.g. occur when a subscriber isroaming in another IMS network.

It is important to identify the intended emergency session as soon aspossible, because the network and the UE need to perform some specialactions for performing the emergency session.

SUMMARY OF THE INVENTION

The present invention provides method and system for enabling emergencysessions to be established in a reliable manner.

The invention provides a method and/or system as defined in the claims.

This invention discloses means and functions of how the network candetect an emergency session, how the UE can be informed about it andwhat effects this information has on later session setup.

The invention provides among others a Network-identification of anemergency session initiated by a session initiating entity such as auser equipment (UE) including mobile or stationary stations orterminals, or the like.

Even when the user equipment is unable to detect by itself that theinitiated session is an emergency session, it is quickly informedthereon and can then initiate the appropriate steps for establishing theemergency session.

According to a first embodiment of the invention, in order to guaranteeresources at the transport level for the emergency call, a response issent back to the UE immediately after a control means such as P-CSCF hasdiscovered that the session is an emergency session. When the UEreceives such a response it will perform a normal emergency sessionprocedure, e.g. as defined in 3GPP specifications. To execute a normalemergency session, the UE will e.g. obtain or query location informationand send it in the INVITE message and also the UE will activate anemergency PDP context for the session.

The invention enables to identify the session to be an emergency sessionas soon as possible so that the network and the UE can perform thenecessary special actions for the emergency session as quickly aspossible.

In one of the alternative implementations of the invention, the controlentity such as P-CSCF does not respond immediately to UE when it hasreceived an INVITE message from the UE but waits for the reception of amessage, e.g. 183 Session Progress, from an emergency center or anintermediate network entity, and adds to that message the emergencyinformation.

The information about the emergency call is not delayed at all, and thecall establishment is continued in the conventional or any other mannersuch as with the 183 Session Progress message.

Sending an INVITE message takes remarkable radio resources and it is notpreferable to send multiple INVITE messages. Actually there is no delayin session establishment, since UE has not yet started creatingsecondary PDP Context before UE receives the SDP message. This meansthat the indication can be included with high priority for the userplane. If no emergency centre is indicated, a default emergency centermay be chosen.

This invention concerns a situation, in which PDP context activation cannot or will not be performed at first when initiating a session for anyreason, but a message such as an INVITE message is sent first from theUE to the CSCF.

Further details, aspects and advantages of the invention will becomeapparent from the following reference to specific embodiments and theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a method and system in accordancewith the present invention;

FIG. 2 shows a second embodiment of a method and system in accordancewith the present invention;

FIG. 3 illustrates a third embodiment of a method and system inaccordance with the present invention;

FIG. 4 shows an implementation for emergency session processing in anormal case.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

This invention discloses solutions to several problems such as:

The UE is able to activate an emergency PDP context after it has beeninformed about the session characteristics. This is important to gethigh priority for the PDP context in the GPRS (General Packet RadioService) and RAN (Radio Access Network).

The UE sends location information after it is being informed about thesession characteristics (it is assumed that location information is notsent in every INVITE message). The location information is used forselecting the most suitable Emergency Centre (EC).

FIG. 1 shows an embodiment of the invention which includes a calloriginating element, i.e. a session initiating element, such as a mobilestation (UE) 10, and a network which comprises a serving network elementsuch as a Serving GPRS Support Node (SGSN), and a further controlelement such as a Call State Control Function (CSCF) or Proxy Call StateControl Function (P-CSCF) 11. The further network elements necessary forcompleting an IP multimedia session such as a terminating element, agateway node if needed, a subscriber information register such as a homelocation register (HLR) or home subscriber server (HSS), etc. are knownto the skilled man and are therefore neither shown nor described in moredetail. Generally, a MSC (Mobile Switching Centre, not shown) may returnto UE a Call Proceedings message which contains a Priority informationfield defining also EC (Emergency Centre).

In all embodiments described above or below, the UE 1 may be equippedwith a USIM (User Services Identity Module).

The embodiments shown in FIGS. 1, 2, and 3 relate to aNetwork-identified emergency session.

A solution to guarantee resources at the transport level to perform theemergency call is to respond back to the UE 10 immediately after anetwork entity, e.g. a control means such as P-CSCF 11, has discoveredthat the session is an emergency session. When the UE 10 receives theresponse, i.e. is informed, by the network, on the initiated sessionbeing an emergency session, it will perform normal emergency sessionprocedure, e.g. as defined in 3GPP specifications.

FIG. 1 shows the solution at a general level.

In step 1, the UE 10 sends a session initiation message, e.g. an INVITEmessage of SIP (Session Initiation Protocol), which indicatess anidentifier, e.g. the E.164 number or LN (logical name), of the calledentity, to the P-CSCF 11.

In a step 2, the P-CSCF 11 analyses the number or LN. When detectingthat a normal session is to initiated, a normal connection procedure iscontinued. When, however, the P-CSCF 11 discovers that the call isemergency call, steps 3 to 6 shown in FIG. 1 are performed.

In step 3, a response is sent to the UE 10 indicating that the sessionis an emergency session.

Step 4: The UE 10 returns an acknowledgement message ACK to the P-CSCF11.

In an optional step 5, the UE 10 may inform the user that the session isemergency session, e.g. by displaying an appropriate message on adisplay of the UE 10.

Then, a normal emergency session is executed (performed) as indicated bystep 6. The execution of a normal emergency session means that the UE 10will e.g. obtain location information and send it in the INVITE messageand also that the UE 10 will activate an emergency PDP context for thesession.

The response message at step 3 can be a new message, or an existing SIPmessage or other known message can be used. The information in theresponse message may be a new parameter in SIP protocol, but an existingparameter may also be used.

FIG. 2 shows a solution in which, in step 3, a SIP 302 message “MovedTemporarily” is used as response. The parameter value in the 302 messageindicates that the session is an emergency session. The parameter maye.g. be “Contact: sip:emergency@visited.cscf.com”. This value can e.g.be used in SIP URI when sending a new INVITE message to P-CSCF 11, orthe UE 10 just generates a new INVITE message with the indication of anemergency session. Another alternative can be to use the SIP NOTIFYmethod.

Apart from the above discusion, the embodiment shown in FIG. 2 has thesame structure and functioning as the one of FIG. 1.

FIG. 3 illustrates another embodiment of the invention. In addition tothe UE 10 and the P-CSCF 11, a Serving CSCF (S-CSCF) 12 and an EmergencyCentre (EC) 13 are shown. The embodiment according to FIG. 3 provides analternative functioning as compared to the embodiments of FIGS. 1 and 2.

In order to achieve a very fast session establishment the P-CSCF 11 doesnot respond back to the UE 10 immediately after P-CSCF 11 has discoveredthat the session is an emergency session. On the contrary it continuessession establishment and optionally, if possible, the P-CSCF 11 adds anindication of emergency session to the messages generated by P-CSCF 11for ensuring high priority treatment of the messages.

The details of the procedure are shown in FIG. 3. Taking account of thenature of emergency session it is highly desirable not to add anyadditional delay also in case of abnormal situations to sessionestablishment. By using the alternative of FIG. 3, it is possible toavoid the transfer of another INVITE message over the air interface,which is probably the largest and slowest message and thus verytime-consuming.

The response message (in SIP, preferably a message “183 Progress”) tothe UE 10 preferably includes an indication of emergency session. Thisallows to activate an emergency PDP context for the session.

If there should not exist location information in S-CSCF 12 (or therelevant server) to select an emergency center 13, the S-CSCF 12 (orrelevant server) will select an emergency center 13 without locationinformation of the user (e.g. it selects a default emergency center,nearest emergency center or it may use some other technique to selectthe emergency center e.g. based on the address of P-CSCF 11.

As shown in FIG. 3, in step 1, the UE 10 initiates a sessionestablishment and sends a session setup message, e.g. an INVITE message,to the P-CSCF 11. The P-CSCF 11 analyses the number or logical name (LN)of the called party/entity indicated in the session setup message, anddiscovers that the call is an emergency call. The P-CSCF 11 may add anindication of emergency session to the INVITE message (it is alsopossible that other elements add this indication of emergency session tothe INVITE message).

In step 2, the INVITE message is forwarded to the S-CSCF 12.

In Step 3, the S-CSCF 12 selects an emergency center (EC) 13 andforwards the INVITE message to the EC 13.

Step 4: The EC 13 responds to the INVITE request by returning a responsesuch as SIP 183 “Session Progress” to the S-CSCF 12. The subset of themedia flows shown in steps 4 to 6 indicates that messages are returnedback to originating endpoints proposing an EC 13 for providing support,or requesting the emergency session.

Step 5: The S-CSCF 12 forwards the response such as SIP 183 “SessionProgress” back to the P-CSCF 11.

Step 6: The P-CSCF 11 forwards the response such as SIP 183 “SessionProgress” back to the UE 10. The response includes the indication ofemergency session. The UE 10 thus learns that this session is anemergency session and can act properly.

The circles and ovals shown in FIG. 3 mean “Emergency call detected,Possibility to add an emergency indication”.

FIG. 4 presents a proposal for normal emergency session establishmentfor the case where the UE has USIM. It is assumed that the UE hasactivated a signalling PDP context to the GGSN in the visited PLMN.

In the following, the steps shown in FIG. 4 are described in moredetail, referring to the step numbering of FIG. 4.

-   1. UE may request SAI (Service Area Identity) from SGSN.-   2. SGSN sends response message to UE.-   3. UE sends the SIP INVITE request, containing an initial SDP, to a    P-CSCF determined via the CSCF discovery mechanism. Information    about emergency call is sent in the INVITE message. UE includes the    location information in the INVITE message.-   4. P-CSCF detects that the call is an emergency call using the    information in the INVITE message e.g. by analysing the number or    name requested. P-CSCF selects a S-CSCF in the visited network and    forwards the SIP INVITE request including the information about    emergency call to S-CSCF.-   5. S-CSCF uses the location information to select an appropriate EC.    S-CSCF forwards the request to EC.-   6. The media stream capabilities of the destination are returned    along the signaling path.-   7. S-CSCF forwards the message containing the destination SDP    cababilities to P-CSCF.-   8. P-CSCF authorizes the resources necessary for this session.-   9. P-CSCF forwards the SDP message to the originating endpoint.-   10. UE decides the final set of media streams for this session, and    sends the Final SDP to P-CSCF.-   11. P-CSCF forwards the final SDP to S-CSCF.-   12. S-CSCF forwards this message to EC.-   13. Activate PDP Context Request. The UE activates a PDP context for    the emergency session by sending the Activate Secondary PDP Context    Request message to the SGSN. The UE indicates that the PDP context    is used for an emergency session. For the PDP context, the    Allocation/Retention Priority shall be at once set to the high    value.-   14. The SGSN, when recognising that the PDP context is for an    emergency session, may itself request location information from    SRNC, in order to receive updated or more accurate location    information regarding the UE. SGSN thereafter sends a location    report to Gateway Mobile Location services Centre (GMLC) as    specified in TS 23.271, and the EC may obtain this location    information from GMLC.-   15. Radio Access Bearer Setup-   16. Create PDP Context Request-   17. Create PDP Context Response-   18. Activate PDP Context Accept-   19. UE sends the “Resource Reservation Successful” message to the    terminating endpoint, via the signaling path established by the    INVITE message.-   20. P-CSCF forwards this message to S-CSCF.-   21. S-CSCF forwards this message to EC.-   22. Resources are reserved successfully.-   23. EC sends information about alerting to S-CSCF.-   24. S-CSCF forwards the Ringing message to P-CSCF.-   25. P-CSCF forwards this message to UE.-   26. EC answers the call and sends final 200 OK message to S-CSCF.-   27. S-CSCF forwards final 200 OK message to P-CSCF.-   28. P-CSCF indicates the resources reserved for this session should    now be committed.-   29. P-CSCF forwards final 200 OK message to UE.-   30. UE starts the media flow for this session.-   31. The calling party responds to the 200-OK final response with a    SIP ACK message which is sent to P-CSCF.-   32. P-CSCF forwards the SIP ACK message to S-CSCF-   33. S-CSCF forwards the ACK message to EC.

Although the invention has been described above with reference tospecific embodiments, the scope of protection of the invention intendsto cover all modifications, omissions, additions and amendments of thedisclosed features as well.

The teaching according to the invention is preferably implemented in anAll-IP Network but may also be employed in networks of various othertypes, i.e. in IM, GPRS and UMTS domains.

1-32. (canceled)
 33. A network element, comprising: a transmitting unitfor initiating a communication session by transmitting a message to anetwork entity, wherein the message indicates and identifier of a callentity; a receiving unit for receiving a response from a network entity,said response informing the network element that the initiated sessionis an emergency session after the network entity as analyzed thereceived identifier as requiring an emergency sessions: wherein thereceiving unit receives the information after the network entity hasinformed an emergency center regarding the existence of the emergencysession, and wherein said information thereby establishes acommunication between the network element and an emergency center.
 34. Anetwork element as recited in claim 33, further comprising: an executionunit for executing the emergency session upon receipt of the informationfrom the network entity.
 35. A network element according to claim 33,wherein the execution unit transmits location information of the networkelement to the network entity.
 36. A network element according to claim34, wherein the execution unit activates an emergency packet dataprotocol context for the emergency session.
 37. A network elementaccording to claim 33, wherein the receiving unit is configured toreceive information which includes a parameter indicating an address ofthe network entity with which the emergency session is to beestablished.
 38. A network element, comprising: a receiving unit forreceiving a message from a user equipment, wherein the message indicatesan identifier of a call entity: an analyzing unit for analyzing thereceived message and identifier; a transmitting unit for transmittinginformation to the user equipment indicating that the initiated sessionis an emergency session.
 39. A network element as recited in claim 38,wherein said a network element comprises a proxy-call state controlfunction (P-CSCF).
 40. A network element as recited in claim 38, whereina receiving unit is configured to receive an emergency sessionre-initiation message.
 41. A network element, comprising: a receivingunit for receiving a message from a user equipment, said messageindicating an identifier of a call entity; an analyzing unit foranalyzing the received identifier; a transmitting unit for transmitting,when the analyzing unit detects that the session to be initiated is anemergency session, information to be sent to an emergency center, withthe information informing the emergency center of an emergency sessionto be established, wherein the information to be sent to the emergencycenter will initiate a notification to the user equipment.
 42. A networkelement is recited in claim 41, wherein the receiving unit, analyzingunit, and transmitting unit are configured to establish the emergencysession between the user equipment and the emergency center.
 43. Anetwork element is recited in claim 41, wherein the network elementcomprises a proxy-call state control function.
 44. A network element,comprising: a receiving unit for receiving a message from a userequipment, said message indicating an identifier of a call entity; ananalyzing unit for analyzing the received message and identifier; atransmitting unit for transmitting, when detected that an emergencysession is to be initiated, information to the user equipment that theinitiated session is an emergency session, and for informing anemergency center that the emergency session is to be established;wherein said a transmitting unit returns the information from the userequipment after receiving a response from the emergency center, whereinthe network element thereby establishes the emergency center between theuser equipment and the emergency center.
 45. A network element asrecited in claim 44, wherein the network element is configured toactivate an emergency packet data protocol for the session.
 46. Anetwork element as recited in claim 44, wherein the transmitting unit isconfigured to transmit the message to the user equipment including aparameter indicating an address of an entity to be addressed forestablishing the emergency session.
 47. A user equipment, comprising: atransmitting unit for transmitting a message to a call controllingnetwork element, said message initiating a session by indicating anidentifier of a call entity; a receiving unit for receiving returnedinformation from the call controlling network element, said returnedinformation containing instructions from the call controlling network toinitiate an emergency session, wherein said transmitting unit isconfigured to re-initiate the emergency session by resending theinformation to the call controlling network.
 48. A user equipmentaccording to claim 47, wherein the transmitting unit is configured totransmit a message to a control controlling network element whichcomprises a proxy-call state control function.
 49. A user equipment,comprising: a sending unit configured to send a message to a networkentity to initiate a session, the message indicating an identifier of acall entity; a receiving unit configured to receive, when the session tobe initiated is an emergency session, and information informing the userequipment that the initiated session is an emergency session; said userequipment further comprising an initiating unit configured to initiateexecution of an emergency session upon receipt of said information. 50.The user equipment is recited in claim 49, when the initiating unitfurther comprises an obtaining unit configured to obtain locationinformation of the user equipment, and to send the location informationto a network entity.
 51. The user equipment is recited in claim 49,wherein the transmitting unit is configured to send the messageincluding a parameter indicating an address of a network entity to beaddressed for establishing an emergency session.
 52. A user equipment isrecited in claim 49, wherein the sending unit is configured to send andacknowledgement message to a call controlling network element inresponse to the receiving unit receiving the information informing theuser equipment that the initiated session is an emergency session.
 53. Auser equipment is recited in claim 49, wherein the initiating unit isconfigured to execute a new an emergency session upon receipt of theinformation, wherein the new emergency session provides additionalnetwork resources for an emergency call.